1891-92-] 



On the Dissociation of a Lichen. 



35 



the siphon ; and as spores of algse are very common in the 

 purest of natural water, one feels some doubt as to the results 

 of the experiments. Curiously enough, these observers advo- 

 cate a theory the contrary of Schwendener's : they believe that 

 unicellular alga? are freely vegetating lichen cells. 



Quite recently an Italian botanist (' Nuov. G-ior. Bot. Ital.,' 

 1890) noticed the natural dissociation of a lichen (Lecanora) 

 growing on an old wall. There were, he says, patches of a 

 deep green colour caused by masses of an alga (Protococcus). 

 He attributes the dissocation to excessive humidity, which 

 hindered the fungus 

 from putting out its 

 short filaments to lay 

 hold of the gonidia. 



Now I come to my 

 own experiments. 

 Two years ago I took 

 some test-tubes and 

 arranged small tubes 

 to pass into them, as 

 is shown in the ac- 

 companying figure. 



Into the expanded 

 part of one of the 

 small tubes sterilised 

 cotton-wool was 

 pushed ; that tube 

 passed down to the 

 bottom of the test- 

 tube : another small 

 tube passed just un- 

 derneath the cork in- 

 side, and outside was 



bent over to be parallel with the test-tube. These were some- 

 what longer than is represented in the figure. The test-tubes 

 were half filled with water, having a little of Sachs' nutritive 

 fluid added to it, and this was repeatedly boiled to destroy spores, 

 &c. The water was aerated by attaching the tube not containing 

 the cotton wool to an aspirator, air being pulled through it for 

 several minutes. Small pieces of lichen (Physcia parietina), 



Nutritive 

 Fluid" 



